1. Field of the Invention
The present invention relates to a sensor abnormality detecting method of detecting an abnormality in fluctuation in a sensor output signal due to contact failure of a sensor for detecting a control amount of a control object. In particular, the invention relates to an electronic throttle control apparatus including a sensor abnormality detecting unit that detects an abnormality of a throttle position sensor for detecting an opening amount of a throttle valve set in an intake pipe of an internal combustion engine for an automobile using the sensor abnormality detecting method.
2. Description of the Related Art
In an electronic control throttle system mounted on a vehicle, an opening of a throttle valve is detected by a throttle position sensor and a target opening of the throttle valve is set on the basis of an accelerator opening and an operation state of an internal combustion engine. The electronic control throttle system subjects a throttle opening to feedback control using a motor-driven throttle actuator or the like such that an actual throttle opening coincides with the target opening.
In this case, for the purpose of improvement of fail safety, the throttle position sensor and an accelerator position sensor are constituted by multiple systems. The multiple system sensors carry out throttle opening control, abnormality monitoring, and the like at the time of normal operation while comparing plural sensor output signals.
As a prior art document concerning detection of an abnormality of a throttle position sensor, for example, there is JP-A-2001-303976.
JP-A-2001-303976 describes as follows. In a throttle control apparatus for an internal combustion engine disclosed in JP-A-2001-303976, “even if a throttle opening signal from the throttle position sensor is judged as abnormal because of instantaneous contact failure, external noise, or the like, a state in which energization to an electric motor is allowed is maintained until the abnormal state lasts exceeding a first predetermined time. Thus, even if the throttle position sensor falls into an instantaneous abnormal state, an operation state of an internal combustion engine is not affected. Therefore, drivability is not spoiled.”
“When the abnormal state of the throttle position sensor is detected continuously for the first predetermined time or more, energization to the electric motor is stopped once and a throttle is kept at a predetermined mechanical opening. Thus, it is possible to prevent a careless increase in the number of revolutions of the internal combustion engine or an engine trouble. When the abnormal state of the throttle position sensor is solved before a second predetermined time longer than the first predetermined time elapses, the throttle control apparatus can return to normal throttle control by resuming energization to the electric motor.”
However, in JP-A-2001-303976, when a deviation between two throttle opening signals in the multiple system constitution and a deviation between two accelerator opening signals in the multiple system constitution deviate from predetermined values set in advance, respectively, and this state continues for the first predetermined time or more, an abnormality of the throttle position sensor and the accelerator position sensor is detected, energization to the electric motor is temporarily stopped, the throttle is kept at a predetermined mechanical opening, and energization to the electric motor is resumed when the abnormal state is solved before the second predetermined time elapses.
Therefore, in an abnormal state in which sensor output signals fluctuate repeatedly because of contact failure or the like of the sensors, abnormality detection cannot be performed when the fluctuation in the sensor output signals is shorter than the first predetermined time. When the fluctuation is longer than the first predetermined time and shorter than the second predetermined time, since the stop of energization to the electric motor and the resumption of energization are performed repeatedly, an operation state of the internal combustion engine is affected to deteriorate drivability. In the worst case, for example, a careless increase in the number of revolution of the internal combustion engine and an engine trouble occur.
Since an abnormality is detected by comparing a deviation between two sensor output signals and a predetermined abnormality judgment value set in advance, it is necessary to set the abnormality judgment value taking into account all operation states. Thus, the abnormality judgment value has to be a large set value having an allowance.
In order to prevent misjudgment for transient noise, a judgment time has to be a large set value having an allowance.
Moreover, when the two sensors use a power supply and a ground in common, it is difficult to perform abnormality detection of the sensors concerning abnormalities such as fluctuation in two sensor output signals in the same phase due to contact failure in a power supply terminal and a ground terminal serving as common terminals and repeated fluctuation in a sensor output value due to contact failure of the sensors. Thus, a detection ability for a sensor abnormality falls.